Lightweight polymethylene terephthalate fabric produced by alkali treatment



March 25, 1952- D'A. H LIGHTWEIGHT POLYMETHYLENE TEREPHTHALATE FABRIC PRODUCED ALKALI TREATMENT Filed Aug. 8; 1949 LOSSCAW WEIGHT FIG. I.

% LOSS IN WEIGHT 0 a .HOURS OF TREATMENT FIG. 3.

.HALL Iii-A1. 2,590,402

0.05 0.075 O.l. THICKNESS 0F FARR/6 //v MM 0 2 4 e a lo HOURS OF TREATMENT FIG. 4.

, Inventors JOHN D'ARCY HENRY HALL BERTRAM'PUSEY RIDGE 5- JOHN R'E'x WHI'NFIELD Atrorneys' Patented Mar. 25, 1952 UNITED STATES PATENT OFFICE LIGHTWEIGHT POLYMETHYLENE TEREPH- THALATE FABRIC PRODUCED BY ALKALI TREATMENT John D'Arcy Henry Hall, Welwyn Garden City; Bertram Pusey Ridge, Potters Bar, and John Rex Whinfield, Hampstead, London, England, assigno'rs to Imperial Chemical lndustries Limited, a corporation of Great Britain Application August 8, 1949, Serial No. 109,078 In Great Britain August 13, 1948 .5 Claims. (Cl. 8 115.5')

v This invention relates to improvements in improving the handle of textile materials composed of these polyesters and also with the production of light weight fabrics from these polyesters.

An object of the present invention is to provide a process for improving the handle of textile materials composed of highly polymerised polymethylene terephthalate. A further object is to produce light weight fabrics composed of the said polyesters. A still further object is the production of very thin fabrics suitable, for example, for use in electrical insulation.

According to the present invention these objects are accomplished by treating fabrics composed of highly polymerised polymethylene terephthalate having 2 to inclusive carbon atoms in the polymethylene chain with an aqueous solution of caustic soda or caustic potash.

We have now found that when fabrics composed of highly polymerised polymethylene terephthalate are treated with a solution of sodium or potassium hydroxide the fabrics undergo a reduction in weight which bears a relation to the time of treatment with the solution. This reduction is uniform throughout the material.

The following examples illustrate but do not limit the scope of our invention.

EXAMPLE 1 Small test pieces of fabric, woven from 45 denier polymeric ethylene terephthalate yarn, were immersed in a vessel containing boiling aqueous caustic soda. The solution contained 4% by weight of caustic soda and the fabric was treated for periods of 1 and 1 hours. The thickness of the fabric before and after treatment was tested on a dial type thickness guage and the breaking load of the yarns was determined on a pendulum type single thread tester. Table 1 gives the average of a number of results obtained.

Table 1 hm boiling After boilin fifig in 4% NaOH in 4% NaOH for 1 hour for 1% hours Percent loss in wcight 19 60 Thickness in mms 0. 1 0. 075 0. 044 Breaking load in gins.

(warp yarns) 309 249 103 In the attached drawings Fig. 1 is a graph in t l which the percent loss in, weight of the fabric is plotted against the breaking load in gms. and in Fig. 2 the percent loss inw'eight is plotted against the thickness of the fabric in The vertical axis in each case represents the percent loss in weight. g e V H H 'It will be observed thatthe thickness of the fabric and the breaking load are, within the limits of accuracy of the testinversely proportional to the loss in weight of the fabric.

EXAMPLE 2 A locknit fabric made up of denier polymeric ethylene terephthalate yarn was treated in a 4.6

by weight caustic soda solution at 91 C, on a winch machine, for varying periods of time.

Table 2 shows the average of a number of results obtained.

Table 2 Hours of Treatment 0 2% I 4 5 9% Percent Loss in Weight 0 17 30 64 Thicknessinmms 0.3 0.25 0.22 0.14

In the attached drawing Fig. 3 is a graph showing the relationship between hours of treatment and. percent loss in weight and Fig. 4 is a graph showing the relationship between hours of treatment and the thickness of the fabric in mms. In each case the horizontal axis represents the hours of treatment.

From these graphs it is apparent that the percent loss in weight is directly proportional to the time of treatment and that the thickness of the fabric is inversely proportional to the time of treatment. Thus the reduction of thickness is proportional to the time of treatment.

The polyester is not degraded by the alkaline solution but is gradually removed from the surface of the filament. In this respect we believe these polyester fibres to be unique among textile fibres. The examples show that the strength of the fabric is reduced proportionately to the amount of polyester removed from the surface of the constituent yarns.

Treatment in a'solution of the alkali metal hydroxide may take place under atmospheric pressure using for example, concentrations between 4 and 20% by weight of sodium or potassium hydroxide in the solution. It is preferred that the temperature should be at least 60 so that the process takes place reasonably quickly. If desired, the fabric or other material may be treated under pressure, e. g. in a pressure kier boiler. Under these conditions lower concentrations of the alkali. metal hydroxide may be used. By a series of simple tests it is possible to ascertain the conditions required to reduce the thickness of the material as desired, for example by preparing graphs of the type i1- lustrated in Fig. 4 wherein time of treatment is plotted against the thickness of the fabric. Caustic soda is the preferred reagent for use in the process of this invention because of its cheapness and the fact that it is already used extensively in the textile trade. It will be appreciated that the weaker the concentration of alkali the greater the time required to reduce the thickness of the fabric.

The fabric may 'be treated by any of the methods commonly used in the art for the liquid treatment of fabrics, e. g. by using a jig or winch. As with allsuch treatments it is essential that there should be. vsuflicient liquid available to permeate the whole fabric uniformly and achieve the desired effect.

- .Fabrics composed of the specified polyesters after treatment according to this invention have greatly improved handle and softness. Fine fabrics soproduced closely resemble silk in handle and other properties.

It is well knownin the art that the weaving or knitting of fine fabrics is more difiicult and expensive than the production of coarser fabrics because of thelower rate of working and the larger number of breakages which occur when using the fine yarns. The process of this invention provides a method of producing fine fabrics which is free fromthe disadvantages of the prior art. I I

Fine fabrics having thicknesses of the order of 0.025 mms. are of importance for use in the insulation of electrical apparatus. Such fabrics may be prepared without difficulty using the process of this invention. If desired, the fabrics so produced may be calendered to reduce the thickness still further.

We claim:

1. A process for producing improved light weight fabrics comprising immersing a fabric composed of a highly polymerised polymethylene terephthalate having 2 to 10 inclusive carbon atoms in the polymethylene chain with an aqueous solution of an alkali selected from the group consisting of caustic soda and caustic potash whereby the weight of the fabric is uniformly reduced, said fabric being immersed in said aqueous solution for a length of time such that a thin, lightweight fabric is obtained.

2. The process of claim 1 wherein the immersion takes place at atmospheric pressure and at a temperature greater than C.

3. The process of claim 1 wherein the immersion takes place at superatmospheric pressures.

4. A process for the production of lightweight fabrics which comprises immersing a fabric composed of a highly polymerised polymethylene terephthalate having 2 to 10 inclusive carbon atoms in the polymethylene chain, in an aqueous solution of an alkali selected from the group consisting of caustic soda and caustic potash, said aqueous solution being at a temperature greater than 60 0., whereby the weight of the fabric is uniformly reduced, the fabric being immersed in said aqueous solution for a time such that a thin, lightweight fabric is obtained.

5. The process of claim 4 wherein said fabric is composed of polymeric ethylene terephthalate.

JOHN DARCY HENRY HALL. BERTRAM PUSEY RIDGE.

JOHN REX WHINFIELD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Chemical Abstracts, 1942, volume 36, page 21- 8 /Teryl. (Copy in Patent Oflice Library.) 

1. A PROCESS FOR PRODUCING IMPROVED LIGHT WEIGHT FABRIC COMPRISING IMMERSING A FABRIC COMPOSED OF A HIGHLY POLYMERISED POLYMETHYLENE TEREPHTHALATE HAVING 2 TO 10 INCLUSIVE CARBON ATOMS IN THE POLYMETHYLENE CHAIN WITH AN AQUEOUS SOLUTION OF AN ALKALI SELECTED FROM THE GROUP CONSISTING OF CAUSTIC SODA AND CAUSTIC POTASH WHEREBY THE WEIGHT OF THE FABRIC IS UNIFORMLY REDUCED, SAID FABRIC BEING IMMERSED IN SAID AQUEOUS SOLUTION FOR A LENGTH OF TIME SUCH THAT A THIN, LIGHTWEIGHT FABRIC IS OBTAINED 